Sinfar “world” is probably bigger than you expect it to be, probably no one has seen all of it because it is in constant evolution by many builders and it is not meant to be a restricted world but a sandbox.
In general, the entire Sinfar world can be divided into the following parts:
A single Neverwinter Nights Server is enough for most persistent world but Sinfar has so many features and possibilities as well as an active population that it was not enough.
Each Sinfar server has a capacity of 96 players online at the same time and can have very different rules.
Those servers all share the same servervault so they are forced to follow the same items rules, but they can still have different “social” rules.
Sinfar main “hub” first had to be split because of a population issue, this is the main purpose of Sinfar's Outer Isles. So both follow the exact same rules, they are just an extension of each other.
Sinfar PvP rules are very strict, it is why we had the idea to add a server where anyone could PvP anyone. It unfortulately didn't work (yet).
The initial idea was to create a place for people speaking French, but then many english players joined so it became a bilingual server. Then, maybe due to the Dreaded Lands failure it also became the place for factions.
Sinfar main servers must all follwo certain rules, for items but also
So why limit Sinfar to this stupid concept? This is where side servers come.
Anyone can run their own side server (for 20$/month) and they get access to ALL Sinfar features and the full control on if and how they want to use them. They can also, of course, make their own systems.
So Side Servers are all very different, completely independant and are ran by different people, you should check them invidually: https://nwn.sinfar.net/servers/list.
Any server other than Sinfar, Sinfar and Sinfar's Outer Isles, The Dreaded Lands and Arche Terre, is a side server.